The present invention provides an improved solution for co-site antenna interference during live tactical communications of Fleet Synthetic Training (FST) and the like.
FST events are computer assisted warfare exercises provided to help users master the tactical and warfighting skills required when deployed in various combat scenarios. The scenarios vary in geography, terrain, situational distance, etc. During synthetic training exercises, event coordinators send real-time data to communication systems and combatant stations initiating realistic missions and creating tactical problems which are executed in the Live, Virtual and Constructive (LVC) domain. Force responses and reactions are captured and recorded for after-action review and assessment. During synthetic exercises players on the training range communicate with a relay tower which connects them to a training network, as shown in FIG. 1. With this configuration, the capability is provided that allows live players to interact with geographically separated players, and support a unified, training environment in an integrated, and virtual battle space enabled by the network backbone of distributed training.
The relay tower is the communication bridge that performs the transition between Live-to-Virtual (L-V) tactical communication domains in synthetic training environments. The player on the training range uses a tactical radio to communicate with another trainee on a virtual radio through the relay to as shown in FIG. 2. The relay tower allows many players in the live domain, spread over a large area on the training range, a single access point to the training network. In order to be an effective communication bridge that handles multiple tactical nets, the relay tower is installed with multiple radios and antennas that connect to the network to establish communications with the virtual radio system. To complete the live communication link with the tactical field radio, the radio and antenna in the relay tower transmit and receive over a Radio Frequency (RF). Consequently, for the synthetic training to be successful, the communication segment must be transparent to the users (perform realistically), connect radios in the live domain to virtual radios, and provide the required number of frequency nets to support different types and sizes of distributed training exercises.
Difficulties with live communication segments are often experienced during many distributed training events. These problems have surfaced as degraded voice transmissions, increased static during transmissions, and blocked or dropped transmissions. When problems occur with the live communication segment, participation of trainees in the live domain of synthetic training exercises may be reduced by unintelligible or completely blocked tactical communication. This effect may result in a change of the tactical response of the trainees and therefore the outcome of the training exercises thereby making the communications in the live communication segment of the distributed training unreliable. A major cause of problems in the live communication segment of distributed training has been traced to cosite interference which occurs during multiple, simultaneous transmit and receive communications with the relay tower.
Cosite interference is unintentional, mutual interference, usually from multiple in-band, active radio communication paths and typically occurs when communication equipment is in close proximity to a shared platform, such as a communication tower or relay tower. As the physical separation between antennas decreases, cosite interference becomes more probable and significant. Interference of tactical communications is significantly increased when communication equipment is in close proximity, for example co-location of radios and antennas on a common platform such as a relay tower as shown in FIG. 3. During simultaneous communications, the off-channel signal power from a transmitting antenna is much stronger than the on-channel signal power received from a trainee out on the range. Consequently, a large number of radios and antennas occupying a shared platform may cause cosite interference, where the transmission of one signal degrades the reception of another signal resulting in static, broken voice or, in severe instances, completely blocked reception of other tactical communications. These complications are not replicated as encountered in real-world deployment and can interfere with valid training conditions. These types of technical issues have the potential to interfere and disrupt synthetic training events and training objectives.
The fundamental cause of cosite interference is the performance limitations of the radio including the inability of the radio to transmit a signal while simultaneously receiving a signal without limitations, which generally fall into three categories: noise, non-linearity products, and image frequency. The degradation in communication is most often directly related to the distances between the relay tower and the trainees in the field. This issue is referred to as the near-far problem. At the receiver input, the signal strength of the off-channel interfering transmit signal, which is near, is stronger than the on-channel receiver signal from the trainee in the field which is further away. The receiver must process the difference in signal power between the off channel, interfering signal and the on-channel Signal of Interest (SOI). Cosite interference occurs when the signal power ratio of the interference channel SOI exceeds the operating capability of the receiver. The extent of the near-far problem on the communication link is directly tied to two main factors, the range requirements for the training site and the frequencies of the interfering and on-channel signals. FIG. 4 is a graphical sketch of the near-far problem. For transmissions that are a larger distance from the relay tower, the signal-to-interference power ratios are larger (>) and for transmissions that are a shorter distance from the relay tower, the signal-to-noise power ratio is less (<). Cosite interference results when the relay radio is unable to process signal power ratios that are present at the antenna input to the radio. Therefore, it is imperative to isolate antennas to reduce the signal power of the interference signal, which will reduce the negative effects of the near-far problem.
Currently, many relay towers on training ranges use systems that allow assignment of frequency nets to antenna arrays with little or no guidance. Without the incorporation of rules and restrictions, communication hardware implementation must be capable of operating under all assignment conditions to guarantee high quality communication links. Without direction, any combination of resources is possible and the relay tower design is forced to incorporate worst case conditions, i.e. minimum antenna isolation for minimum channel spacing.
Consequently, with no controls in place to isolate antennas, any combination of antennas is possible. That is, without analytical modeling and simulation of the factors that contribute to poor communication link performance, the live communication segment of synthetic training may simply not function. Degraded unreliable or broken tactical communication links may then cause disruptions during training in a distributed exercise. By performing calculations that take into account components of cosite interference tactical communication problems are identified before they occur. Since the quality of a communication net varies for each frequency pair and antenna isolation varies for each antenna pair the assignment of antenna pairs with the most isolation to frequency pairs aids to avert the problem. The challenge is that as the number of radio-antenna combinations increases, the number of possible assignment combinations becomes extremely large. Therefore what is needed is a solution that determines frequency antenna assignments and results in added isolation to supplement radio capabilities and balance range requirements.